This invention relates to a pierceable sealing element for a liquid outlet, especially the ink outlet opening of an ink reservoir in inkjet printing means, which has a piercing area which can be pierced by a hollow needle for removing liquid, and the hollow needle can be surrounded sealed from the outside by the pierced seal element. An ink reservoir for detachable mounting in inkjet printing means with an ink outlet opening which is sealed by one such pierceable sealing element is likewise the subject matter of the invention.
To remove liquid as necessary, for example from an ink reservoir, sealing liquid-tight the outlet or removal opening with a closed sealing element which is intact before use is known. The liquid can be removed by means of a hollow needle which is plunged from the outside into the filled reservoir interior through the piercing area of the sealing element intended for this purpose. These sealing elements are used preferably in inkjet printing systems where the interchangeable ink reservoirs, the so-called ink cartridges, are first sealed on their ink outlet opening with one such pierceable sealing element after filling with ink during manufacture. The inkjet printer has a corresponding hollow needle which pierces the sealing element when the ink cartridge is being used and the ink contained in the ink cartridge can be supplied to the print head.
The important advantage of a pierceable sealing element is that it is sealed tight before the first use, i.e. the first perforation by the hollow needle, so that the liquid contained in the reservoir can neither emerge uncontrolled from the liquid outlet nor evaporate. Especially in ink cartridges is this particularly important since after production and filling with ink in general they are only used after some time. Even when stored for a longer time it must be ensured that neither the ink fill level is reduced nor the consistency of the ink adversely changed by vaporization.
One possibility for implementing a pierceable sealing element consists in the attachment of a liquid-tight and vapor-tight sealing film from the outside on the outlet opening. So that it can be easily pierced, i.e. clears the outlet when the generally relatively blunt hollow needle is plunged through, this sealing film consists of thin, relatively poorly elastic plastic material. In this way, when the piercing area is punctured it is completely ruptured and clears the outlet cross section. One such sealing film however does not perform a sealing function so that in the sealing element there must be additional sealing rings which seal against the outside periphery of the hollow needle so that liquid cannot emerge there uncontrolled along the hollow needle. These arrangements, as are described for example in EP 1 000 753 A1, are relatively complex due to the separate sealing elements.
A less complex version of a pierceable seal is a so-called septum. It has a relatively thick piercing area of rubber or thermoplastic elastomer. This piercing area bursts when the hollow needle is inserted, not over its entire surface in an uncontrolled manner, like a sealing film, but is essentially penetrated only in the cross sectional area of the hollow needle. Due to the elasticity of the rubber or elastomer material, the boundary surface of the puncture channel formed in doing so is pressed against the outside periphery of the hollow needle so that a certain sealing is achieved without additional sealing elements. Moreover when the hollow needle is removed the puncture channel is automatically reclosed. But when examined minutely, it is found that when the hollow needle punctures, the material of the septum is not radially displaced in a uniform manner, but a small lengthwise tear forms. In the area of the ends of the tear however along the puncture channel between the material of the septum and the outside periphery of the hollow needle gusset-like passages are formed. For this reason leaks are inevitable, especially when there is liquid in the container for a longer time, on the septum, as is the case in an inkjet printing systems. Likewise attempts have already been made to mold a piercing area with a reduced material thickness into the septum. But the results are however likewise not completely satisfactory since the seal can likewise be adversely affected by the irregular tear edges in the penetration channel.
In view of the aforementioned problems in the prior art, the motivation for the invention is to make available a pierceable sealing arrangement and an ink reservoir with one such sealing arrangement which has improved functionality with respect to the indicated problems. In particular, sealing to the hollow needle which is improved compared to a septum will be achieved and the production and installation cost will be as low as possible, especially less than in a multi-part arrangement with seals and a separate sealing film.
To solve the aforementioned problem as claimed in the invention an ink reservoir with a pierceable sealing element and a pierceable sealing element of the initially mentioned type are proposed in which the piercing area is surrounded by an annularly peripheral sealing profile which can be twisted in the manner of a torus at least partially around a peripheral line when the piercing area has been pierced, a sealing surface which runs radially on the inside being formed.
As claimed in the invention a novel sealing element is made available which has clearly distinguishable operating areas in one component. One particular feature compared to the prior art consists in that the two functions, specifically on the one hand the sealing function by a piercing area which can be ripped open only if necessary and on the other hand the sealing function with respect to the hollow needle in the penetrated state, are implemented by a functionally connected arrangement of the central piercing area with a special sealing profile which is formed or activated only when pierced.
In the initial state, before the sealing element has been pierced by a hollow needle, the piercing area extends for example in the form of a thin membrane over the opening cross section of an annular sealing profile which is inserted for its part tightly into the outlet opening, for example the ink outlet opening of an ink cartridge for an inkjet printing means. If from the outside a hollow needle is plunged into the piercing area, it tears or bursts so that the liquid outlet is cleared for example for ink removal through the hollow needle.
As was detailed initially, it can be assumed that the piercing channel or the tear edges of the piercing area at best provide for unsatisfactory sealing of the hollow needle in the outlet opening. The special advantage of the invention at this point consists in that when the piercing area is ripped open and with the associated radial bending-up of the separate parts of the piercing area which are connected in their outer edge areas to the sealing profile which runs peripherally there, the sealing profile is cleared and activated for sealing of the hollow needle. To do this, the sealing profile as claimed in the invention is actively manipulated by its being ripped open, i.e. the piercing of the piercing area, such that it is twisted toroidally on its inner periphery in the puncture direction of the hollow needle, i.e. that the surface areas of the sealing profile which are outside with respect to the puncture direction are swivelling radially to the inside in the direction of the pierced opening in an arc-shaped swivelling motion. In this way the actuation or formation of the sealing profile takes place such that annular surface areas of the sealing profile which are initially farther to the outside are swivelled to the inside, by which a defined sealing surface which runs radially to the inside is formed. This surface can uniformly adjoin the surface of the inserted hollow needle over the periphery. Because this sealing surface is a defined surface area which is uniformly smooth especially over its periphery, the sealing of the hollow needle is especially good. Due to the toroidal connection, moreover the edge areas of the piercing area which are separated from one another are swivelled away axially from this active sealing surface of the sealing profile so that they cannot adversely affect the sealing. This avoids the adverse effect which is occasionally observed in a combination of sealing films with sealing rings, specifically the remainder of the sealing film is retracted between the seal and the hollow needle upon puncturing. As a result of the clear functional connection of the piercing area to the peripheral sealing profile as claimed in the invention these disadvantages are effectively avoided.
The sealing element as claimed in the invention thus combines the advantages of a simple septum, specifically production and installation with low cost, with the advantages of a pierceable sealing film over a separate sealing arrangement, specifically the preparation of defined radial sealing surfaces for sealing the hollow needle. This improved functionality results first of all in that the deformations which occur when the piercing area is pierced and the associated forces are converted in a controlled manner into active manipulation or formation of the sealing profile. When the piercing area is pierced an optimized sealing arrangement is essentially automatically formed.
The sealing profile as claimed in the invention is preferably made as a sealing bead. The latter is formed by a notch which is trough-shaped in cross section and which runs annularly peripherally. This sealing bead is preferably axially opened to the inside with respect to the puncture direction. From the outside, therefore from the puncture side, the sealing bead thus forms a projecting sealing bulge.
The sealing bead is arranged such that the piercing area is connected to the inside edge of the sealing bead which is connected on its outside edge to the mounting element. This mounting element can be made as a tube section which can be fixed in the outlet opening. For example, one such sleeve-shaped mounting element can be inserted into the likewise tubular ink outlet of an ink reservoir and fixed therein.
In the above described embodiment, the sealing bead after splitting the piercing area when the hollow needle on its inner edge is inserted is bent moreover radially to the outside and drawn in the puncture direction by the arising friction forces of the suspended remainders of the piercing area. In this way the arched bottom area of the bead is twisted toroidally. In particular the sealing bead with the U-shaped cross section assumes the shape of an O ring on its inner periphery. Due to the swivelling and pulling motion of the split parts of the piercing area it is narrowed so that an especially internal opening cross section of this O ring-like seal yields moreover good radial sealing of the inserted hollow needle.
One especially advantageous embodiment of the invention as an alternative to the above described sealing bead calls for the sealing profile to be made as a sealing ring. Before the first use, i.e. before the first insertion of the hollow needle, the through opening of this sealing ring is sealed by the piercing area. This piercing area is made as a membrane-like, thin film which is connected to the inside edge of the sealing ring and has a smaller material thickness than the profile cross section of the sealing ring. The function and the resulting advantages of the sealing ring correspond essentially to the sealing bead. Upon piercing, first the puncture area is split by the hollow needle so that the through opening of the sealing ring is cleared. The friction forces acting upon axial insertion between the outside periphery of the inserted hollow needle and the inside periphery of the sealing ring twist this sealing ring around a peripheral line in the shape of a torus. This results in that the inside periphery, where the piercing area is connected to the sealing ring, is turned away from the surface of the inserted hollow needle, while moreover a peripheral sealing area is swivelled to the inside, surrounding the hollow needle tightly on the outside.
To achieve the aforementioned effect, the inside diameter of the sealing ring which is sealed first with the piercing area is chosen to be somewhat smaller than the outside diameter of the hollow needle. In this way, on the one hand it is ensured that the friction forces between the hollow needle and the sealing ring are large enough during puncture to twist the sealing ring around the peripheral line in the shape of a torus. On the other hand, the sealing ring consisting of rubber elastic material in the punctured state under radial pretensioning adjoins the hollow needle; this benefits good sealing action.
The sealing ring can have a round, preferably circular cross section. With the circular cross sectional profile a torus shape arises which corresponds to a classical O ring which can in the conventional manner adjoin a peripheral linear sealing surface on the hollow needle to form a good seal. In an individual case it can furthermore be advantageous for the sealing ring to have a rounded shape which deviates from the circular, for example an involute shape. In this way for example defined force ratios can be achieved between the hollow needle and the sealing ring upon puncture and after toroidal rerolling in the sealing state.
The sealing ring can moreover be connected via a peripheral, thin crosspiece to a mounting element. The mounting element is for example, as in the sealing bead, a tubular section, with the sealing element as claimed in the invention molded in one piece into its through cross section. The externally peripheral crosspiece is clearly thinner than the profile cross section of the sealing ring. In this way it can be swivelled easily when the hollow needle is inserted around a peripheral line which lies in the area of this thin crosspiece for executing the toroidal twisting as claimed in the invention.
In the version with the sealing ring the sealing profile can be made symmetrical with respect to the piercing plane. This piercing plane is defined by the piercing area. There is mirror symmetry to this surface when the sealing profile is made as an O ring with a circular profile cross section, the attachment to the mounting element taking place on the outer peripheral line and the piercing area being peripherally connected to the inside edge of the sealing ring. The symmetrical arrangement has advantages in production engineering. Moreover, installation is simplified thereby.
The piercing area can be made as a thin membrane with a smaller material thickness than that of the sealing profile or the sealing bead. Alternatively, the piercing area can have essentially the same material thickness as in the area of the sealing bead, but then can be provided with molded-in scored areas with a reduced material thickness. They are made for example as notches arranged in a line or cross-shape.
Preferably the connecting area between the piercing area and the sealing profile has a reduced material thickness. In this way, a type of annularly peripheral film hinge is formed which ensures that the separated areas of the sealing area when the hollow needle is inserted in the insertion direction are swivelled away from the sealing area of the sealing profile without the sealing profile being deformed in an uncontrolled manner.
Preferably the sealing element is produced from elastic material, such as natural or synthetic rubber materials or thermoplastic elastomers. But preferably the piercing area, the sealing element and the mounting element are made in one piece with one another. In this way not only simple and economical production, but also installation with low cost is enabled.